[Xperia Z1 Compact Android Development] foresto:
I'm not disputing your experience, but we should be careful not assume that our own success in one particular scenario guarantees that someone else will succeed in a similar but slightly different scenario. For example, I *was* able to boot TWRP before I used Sony's official tool to update the bootloader, but only if I had TWRP on the recovery partition *and* a matching kernel installed on the boot partition. When I swapped out that kernel, or erased the boot partition, TWRP no longer worked. In other words, what seemed like success turned out to be an illusion, as TWRP was not in fact booting from the recovery partition independent of the other partitions. (I suspect it was still relying on some part of Sony's "fake" recovery system, as used before the bootloader update became available.) It was definitely not providing full and correct functionality, and its utility as a recovery system was therefore severely crippled.

Yes, there is, but I think it's important not to characterize the problem as something that only affects people with old stock firmware. Users with new non-stock firmware are also affected (if they never installed newish stock firmware), and if they think the problem described here only affects stock firmware users, then they are likely to ignore the instructions for solving it and end up with a very unpleasant surprise. Let's just make sure the warning catches the attention of everyone likely to need it.

No. I had no issues with cm-12.1. I flashed it with fastboot and the old fake recovery, and I used it for quite a while without ever using TWRP or installing any stock firmware updates.

The only reason I installed TWRP at all was to try this ROM. I tested it more thoroughly than some people probably do, because I like to discover problems early, before they become harder to solve. In doing so, I learned about the problems that I reported in this thread.

In my experience, Sony's tool is the only reliable way to fix it. Another tool might fix the problem, but if not, or if such a tool requires installing a firmware image from an untrusted source, then using the official tool is absolutely worthwhile. Also, since an incomplete bootloader update can easily go undiscovered (as described in my first paragraph of this post), I would suggest using the official tool by default if it is convenient to do so, or else using another tool (with a verified official firmware image) and then making sure that TWRP boots correctly from the recovery partition even when the boot partition has been erased.

---------- Post added at 15:38 ---------- Previous post was at 15:21 ----------

I'm referring to the tool known as Emma. It comes from here. I think the current downloaded file name is Xperia_Flash_Tool_Setup_18w47.exe, and an older version was Emma_Setup-2.15.13.201509141241.exe.

I don't know if there is a Mac version of that tool, and if there is then I'm sorry for assuming otherwise, but it doesn't matter in the context of my original comment. When someone mentions keeping Windows around in order to use the tool, it implies to me either that they couldn't find a Mac version or that they couldn't use it. Maybe they run linux, for example.