Bug in parser?

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POSTGRESQL BUG REPORT TEMPLATE
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Your name : Gerhard Dieringer
Your email address : Gerhard(dot)Dieringer(at)nexgo(dot)de

System Configuration
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Architecture (example: Intel Pentium) :Dual Intel Pentium II

Operating System (example: Linux 2.0.26 ELF) : Linux 2.2.16

PostgreSQL version (example: PostgreSQL-7.3.3): PostgreSQL-7.3.3

Compiler used (example: gcc 2.95.2) : gcc-Version 3.3

Please enter a FULL description of your problem:
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Inconsistent results when calling '+' operator with text arguemts
The last 4 results (f.e. '1' + '2' -> 'c') are very strange.

Please describe a way to repeat the problem. Please try to provide a
concise reproducible example, if at all possible:
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select 1 + '2' as result;
result
--------
3
(1 row)

select 1 + '2.3' as result;
psql:error.sql:2: ERROR: pg_atoi: error in "2.3": can't parse ".3"
select 1.5 + '2' as result;
result
--------
3.5
(1 row)

select 1.4 + '2.3' as result;
result
--------
3.7
(1 row)

select '1' + '2' as result;
result
--------
c
(1 row)

select '1' + '2.3' as result;
result
--------
c
(1 row)

select '1.5' + '2' as result;
result
--------
c
(1 row)

select '1.4' + '2.3' as result;
result
--------
c
(1 row)

If you know how this problem might be fixed, list the solution below:
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Sorry :-((