ELSE was unexpected at this time

I frequently work on the Windows command line within ConEmu and occasionally, after working in a given window for some time, get the following unexpected error:

ELSE was unexpected at this time.

Currently, it occurred after pasting about 150 lines of rm commands (may be unrelated).

Once I get that error, I cannot use the ELSE statement in that window; I must start a new shell process, at which point my scripts work as expected. For example, once that error occurs in a window, I observe the following:

C:\> IF DEFINED AN_ENV_VAR (ECHO YES) ELSE ECHO NO
ELSE was unexpected at this time.
C:\> IF NOT DEFINED AN_ENV_VAR (ECHO YES) ELSE ECHO NO
ELSE was unexpected at this time.
C:\> IF DEFINED AN_ENV_VAR (ECHO YES)
C:\> IF NOT DEFINED AN_ENV_VAR (ECHO YES)
YES

A new shell gives expected results:

C:\> IF DEFINED AN_ENV_VAR (ECHO YES) ELSE ECHO NO
NO
C:\> IF NOT DEFINED AN_ENV_VAR (ECHO YES) ELSE ECHO NO
YES
C:\> IF DEFINED AN_ENV_VAR (ECHO YES)
C:\> IF NOT DEFINED AN_ENV_VAR (ECHO YES)
YES

Is there any way to fix the current shell?