Submitted by: @pavel-zotov

1) create database with default page_size (8k)
2) run:
echo recreate table test(s varchar(2039) unique); set count on; insert into test select rpad('', 2039, uuid_to_char(gen_uuid())) from rdb$types, rdb$types; | isql /3333:e30 & gstat -r /3333:e30

Output of ISQL will be like this:

Statement failed, SQLSTATE = 54000
Implementation limit exceeded
-Maximum index level reached
Records affected: NNN

Output of "gstat -r":

TEST (135)
Primary pointer page: 179, Index root page: 185
Total formats: 1, used formats: 0
Average record length: 0.00, total records: 0
Average version length: 0.00, total versions: 0, max versions: 0
Average fragment length: 0.00, total fragments: 0, max fragments: 0
Average unpacked length: 0.00, compression ratio: 0.00
Pointer pages: 1, data page slots: 0
Data pages: 0, average fill: 0%
Primary pages: 0, secondary pages: 0, swept pages: 0
Empty pages: 0, full pages: 0
Fill distribution:
0 - 19% = 0
20 - 39% = 0
40 - 59% = 0
60 - 79% = 0
80 - 99% = 0

Index RDB$8 \(0\)
    Root page: 899, depth: 16, leaf buckets: 119, nodes: 0
    Average node length: 0\.00, total dup: 0, max dup: 0
    Average key length: 0\.00, compression ratio: 0\.00
    Average prefix length: 0\.00, average data length: 0\.00
    Clustering factor: 0, ratio: 0\.00
    Fill distribution:
         0 \- 19% = 1
        20 \- 39% = 118
        40 \- 59% = 0
        60 \- 79% = 0
        80 \- 99% = 0

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All numbers for INDEX section should be zeroes because in fact none records have been added into the table.
PS. gfix -sweep does not help: non-zero values remain in gstat after it.