/.../
/usr/local/pike/7.8.352/lib/modules/Protocols.pmod/HTTP.pmod/module.pmod:161:Got placeholder object when indexing module HTTP with 'Query'. (Resolver problem.)
The problem appears to be the programs and objects mappings in the master. If I replace either, these problems happen. If use the existing mappings from the current master (moved before using replace_master()), things work properly. If I do a shallow copy, things fail, so I'm inclined to believe that somethings holding on to those mappings, perhaps in dirnode().
It could also be that the old master is still called in some cases.
I haven't compared the differences between the two masters, but I know that changes were made to the resolver, correct?
Spontaneously I thought there would be, but there are actually fairly few commits to the master in 7.9 only:
git log --oneline 7.8..7.9 lib/master.pike.in
eac07315 Fixed compat resolver fallback order. fac36c39 Runtime: Changed backtrace representation for event handlers. 9eaaf898 Updated copyright. c5d9a9a6 Removed $Id$. 080e3aa0 Added support for dynamic compile-time macros. 0e22d157 Added RECUR_COMPILE_DEBUG to attempt to help debugging recursive resolver issues. 91ac5642 Ensure _master_file_name is set even without -m. fea47d91 Fixed unbalanced use of INC/DEC_RESOLV_MSG_DEPTH() in dirnode()->low_ind() a63ecdbd Instantiate the fallback codecs instead of using the master directly. 548e838f Improved unregister() to find stuff in joinnodes a bit better. 3032b456 Deprecating pike.ida.liu.se for pike.lysator.liu.se. eb6f0eef master: Restored lost comment. 1a03d133 Clean up some create():s 0e26166a Added compatibility mode for Pike 7.8. 6dd09dad Fixed the codec to handle the Val module values in a good way. 7729dbc4 Improved master compatibility with Pike 7.6. 130970d5 Improved describe_function for top level functions in modules. e15f7f13 Added callbacks to allow overlaying masters to read precompiled code from other sources. 9dcabf1e Give dirnodes and joinnodes real names to improve sprintf output.
I haven't dug around, but I see nothing obvious there that could have a bearing on this problem.