Submitted by: @pavel-zotov

Attachments:
core2018-read_only.fbk
c4748-all-fine.zip

1. Create new database on 2.5.4
2. Run:
2.1 {FB25_HOME}\bin\gfix -mode read_only <this_25database.fdb>
2.3 {FB25_HOME}\bin\gbak -b <this_25database.fdb> <this_25database.fbk>

After that, try to restore .fbk in 3.0:
{FB30_HOME}\gbak -rep this_25database.fbk localhost/3333:C:\FBTESTING\qa\fbt-repo\tmp\this_30database.fdb

On 3.0 SC & CS this will works fine, see gstat after end of this:

C:\FBTESTING\qa\fbt-repo\tmp>C:\1INSTALL\FIREBIRD\fb30sC\gstat.exe -h CORE2018-READ_ONLY-SC.FDB

Database "C:\FBTESTING\QA\FBT-REPO\TMP\CORE2018-READ_ONLY-SC.FDB"
Database header page information:
Flags 0
Generation 16
System Change Number 0
Page size 4096
ODS version 12.0
Oldest transaction 1
Oldest active 2
Oldest snapshot 2
Next transaction 6
Sequence number 0
Next attachment ID 2
Implementation HW=Intel/i386 little-endian OS=Windows CC=MSVC
Shadow count 0
Page buffers 0
Next header page 0
Database dialect 3
Creation date Apr 13, 2015 2:20:52
Attributes force write, no reserve, read only

Variable header data:
    Sweep interval:         20000
    \*END\*

C:\FBTESTING\qa\fbt-repo\tmp>C:\1INSTALL\FIREBIRD\fb30sC\gstat.exe -h CORE2018-READ_ONLY-Cs.FDB

Database "C:\FBTESTING\QA\FBT-REPO\TMP\CORE2018-READ_ONLY-CS.FDB"
Database header page information:
Flags 0
Generation 20
System Change Number 0
Page size 4096
ODS version 12.0
Oldest transaction 1
Oldest active 2
Oldest snapshot 2
Next transaction 8
Sequence number 0
Next attachment ID 4
Implementation HW=Intel/i386 little-endian OS=Windows CC=MSVC
Shadow count 0
Page buffers 0
Next header page 0
Database dialect 3
Creation date Apr 13, 2015 2:21:29
Attributes force write, no reserve, read only

Variable header data:
    Sweep interval:         20000
    \*END\*

=====

But on 3.0 SuperServer it will hang infinite time, with zero CPU load.
ISQL does not react to Ctrl-Break and can be closed only via psKill.exe or pressing 'CLOSE' icon on its window.

FB versions:

WI-V2.5.4.26856
WI-T3.0.0.31780