In PowerShell 3, if there is a signed script block (or script, or localized data file) which is imported (invoked interactively, or parsed using Import-LocalizedData), ALL localized data files (or interactive commands) which are imported/executed after that must be shorter than the previous signed one or they will fail to parse with a TokenAfterEndOfValidScriptText error:
Executable script code found in signature block.
+ CategoryInfo : ParserError: (:) , ParentContainsErrorRecordException
+ FullyQualifiedErrorId : TokenAfterEndOfValidScriptText
NOTE: this bug affects Import-LocalizedData *AND* the "data" keyword in PowerShell scripts.
In PowerShell 4, the bug only emerges when the signature block is cut off (say, if someone accidentally deletes the last line of a signature).
Reproduction steps below apply to PS3 or PS4 (because I don't put a full signature in the reproduction).
This does not affect PS2.