Thanks for your bug report. I decided not to add support for timezone abbreviations for several reasons. Window's own time functions support some abbreviations and not others. There are also many identical abbreviations that stand for different timezones (see here, for example: AMST, AST, BST, CDT, CST, etc.) so using one of these abbreviations could provide an unexpected offset. Also, I have not found a single definitive abbreviations list. Every list I come across includes or excludes abbreviations that exist in other lists.

That said, adding support for offsets like +NNNN and UTC/GMT would work. The only possible issue is that if scripters are already catering for this limitation (considering that $ctime() has always worked this way), adding support for this now would break existing scripts.