z/OS systems-ssl strange behaviour with environment variables

I was trying to use system ssl to write a program to use native z/O TLS facilities. I wasted a couple of hours because it said it could not find my keyring. Then when I collected a trace, it sometimes did not find the file – which did exist as I could list it.

If I used

//START1   EXEC PGM=GSKMAIN,REGION=0M, 
//*  PARM='4000' 
// PARM=('ENVAR("_CEE_ENVFILE=DD:STDENV")/4000') 
//STDENV DD PATH='/u/ibmuser/gskparms' 

When the USS file had

GSK_TRACE_FILE=/tmp/zzztrace.file 
GSK_TRACE=0xff 
GSK_KEYRING_FILE=START1/TN3270 

This worked file

When I used

//START1   EXEC PGM=GSKMAIN,REGION=0M, 
//*  PARM='4000' 
// PARM=('ENVAR("_CEE_ENVFILE=DD:STDENV")/4000') 
//STDENV  DD * 
GSK_TRACE_FILE=/tmp/zzztrace.file 
GSK_TRACE=0xff 
GSK_KEYRING_FILE=START1/TN3270 
/* 

This failed to work.

If I looked in the trace file I had

ENTRY gsk_open_keyring(): ---> Keyring 'START1/TN3270                       ' 

Where it had taken the whole length of the line – and so START1/TN3270 padded with blanks was not found.

The trace file was not /tmp/zzztrace.file, it was /tmp/zzztrace.file padded with lots of blanks!

The answer is to use a environment file in USS, not in JCL or a data set.